1. Field of the Invention
The present invention relates to an organic light emitting display and a manufacturing method thereof, and, more particularly, to an organic light emitting display and a manufacturing method thereof capable of improving image quality of the organic light emitting display.
2. Description of the Related Art
Various flat panel display devices, having less weight and volume than a cathode ray tube, have been developed. A flat panel display device can be a liquid crystal display (LCD), a field emission display (FED), a plasma display panel (PDP), an organic light emitting display (OLED), etc.
An organic light emitting display is a flat panel display device that displays an image using an organic light emitting diode (OLED) to generate light by utilizing the recombination of electrons-holes.
FIG. 1 is a circuit view showing a pixel adopted in an organic light emitting display. Referring to FIG. 1, the pixel includes a first transistor T1, a second transistor T2, a capacitor Cst, and an organic light emitting diode OLED.
The source of the first transistor T1 is coupled to a first power supply ELVDD, the drain thereof is coupled to an organic light emitting diode OLED, and the gate thereof is coupled to a node N1. The source of the second transistor T2 is coupled to a data line Dm, the drain thereof is coupled to the node N1, and the gate thereof is coupled to a scan line Sn.
The first electrode of the capacitor Cst is coupled to the first power supply ELVDD and the second electrode thereof is coupled to the node N1.
Also, the organic light emitting diode OLED includes an anode electrode, a cathode electrode and a light emitting layer, wherein the anode electrode is coupled to the drain of the first transistor T1 and the cathode electrode is coupled to a second power supply ELVSS.
If current flows from the anode electrode of the organic light emitting diode OLED to the cathode electrode thereof, the light emitting layer emits light corresponding to the amount of the flowing current. The equation 1 represents current flowing into the drain of the first transistor T1.
                              I          d                =                              β            2                    ⁢                                    (                              ELVDD                -                Vdata                -                Vth                            )                        2                                              Equation        ⁢                                  ⁢        1            
Here, Id represents the current flowing into the drain of the first transistor T1, Vdata represents the voltage of a data signal, ELVDD represents the voltage of the first power supply transferred to the source of the first transistor, Vth represents the threshold voltage of the first transistor T1, and β represents a constant.
Therefore, the current flowing into the drain of the first transistor T1 flows corresponding to the voltage of the data signal and the threshold voltage of the first transistor T1. However, a difference for the threshold voltage of the first transistor T1 occurs in a process for manufacturing an organic light emitting display, thereby causing unevenness of brightness between pixels.